Disease suppressive effects of resistance-inducing agents against red rot of sugarcane

Red rot caused by Colletotrichum falcatum is one of the most devastating fungal diseases of sugarcane in many tropical countries. In this study, the efficacy of various resistance-inducing agents was evaluated against red rot at two growth phases of sugarcane, i.e., the germination and grand growth phases, for four consecutive cropping seasons (2011–12 to 2014–15) under field conditions. Inducer candidates of both synthetic origin (benzothiadiazole [BTH], salicylic acid [SA], potassium silicate [PSi]) and biotic origin (Colletotrichum falcatum [Cf] elicitor and Reynoutria sachalinensis extract) were evaluated for their efficacy on a red rot susceptible sugarcane cultivar CoC 671. Inducer concentrations that showed significant reduction of red rot lesion length in leaf bioassays without exhibiting direct antifungal activity were used in the field trials. Overall, results of the four field trials indicated that application of BTH (125 μM) and Cf elicitor (60 μg glucose equivalent/ml) were most efficient in reducing disease incidence during the germination and establishment phases against soil-borne inoculum and suppressed disease severity in pathogen challenged cane stalks during the grand growth phase. In addition, other treatments also had significant effects on germination and stalk disease severity. Quantification of C. falcatum biomass in resistance inducer-treated canes by quantitative PCR (qPCR) substantiated the disease suppressive effect of BTH and Cf elicitor. Whereas all resistance inducers significantly increased the cane weight, only BTH and PSi significantly increased the juice quantity. Other juice quality parameters were generally not affected by the inducers.